The continued miniaturization of advanced semiconductor devices requires atomic layer control in both growth and etching processes. Atomic layer deposition (ALD) and atomic layer etching (ALE) techniques can provide the necessary atomic level precision. ALD techniques have been developed for a wide range of materials over the past few decades, and have been extensively adapted by the semiconductor industry. In contrast, the need for ALE techniques has emerged more recently, and ALE methods are still in an early stage of development.
Initial plasma ALE methods have been based on surface activation by halogenation, followed by ion bombardment to remove surface material. Plasma processes have been developed for a variety of materials including Si, compound semiconductors, metal oxides, and carbon materials. The plasma ALE method can further achieve anisotropic etching.
Thermal ALE techniques have also been demonstrated with fluorination and ligand-exchange reactions. Thermal ALE methods have been developed for Al2O3, HfO2, ZrO2, AlN and AlF3. Thermal ALE is capable of providing isotropic etching. In contrast, materials with volatile metal fluorides do not have thermal ALE pathways using fluorination and ligand-exchange reactions because their fluorides are gases. Other materials, such as elemental metals, may fluorinate readily and produce fluoride layers that are too thick for ALE. For these materials, alternative pathways are required for controlled ALE.
There remains a need in the art for methods that allow for ALE to be used in materials resistant to known plasma ALE and thermal ALE techniques. The present invention addresses and meets this need.